CartItemInterface should include customizable_options

[laurentiumagureanu]

Fix all nullable customizable_options

customizable_options: <SelectedCustomizableOption]

to be non nullable
customizable_options: [SelectedCustomizableOption]!

this will fix the BiC introduced in 2.4.1
will also fix the bundle problem which is the only one that's nullable now
[~cspruiell> plz update this description accordingly

!screenshot-1.png|thumbnail!

1. I need to query a user's cart via graphQL and include customizable_options for each cart item.
2. In order to do that now I need to use a fragment for each type implementing CartItemInterface
3. Problem is that BundleCartItem has customizable*options: [SelectedCustomizableOption]! ( not nullable ) while all the other cart item types have customizable*options: [SelectedCustomizableOption] (nullable)

Expected result (*)

1. The customizable_options field should be part of CartItemInterface since all implementing types include it.
2. The customizable_options field should at least use the same type declaration in all implementing types in order to be able to fetch it in the cart query.

Actual result (*)

1. The cart query validation error
   

[dthampy]

@magento export issue to Jira project MC as Bug

[mauragcyrus]

@magento export issue to Jira project MCLOUD as Bug

[magento-engcom-team]

✅ Jira issue (https://jira.corp.magento.com/browse/MCLOUD-7370) is successfully created for this issue.

[korovitskyi]

@magento I am working on this